This application is the national phase filing of PCT Application Serial No. PCT/EP00/12835 which claims priority to German Patent Application No. 100 04 121.3 filed Jan. 31, 2000, which applications are herein expressly incorporated by reference.
The present invention relates to a coil spring and a support bearing arrangement for suspension struts, which support steering knuckels of an automobile.
Suspension struts for automobiles have a shock absorber connected at its upper end to the car body and at its lower end to the steering knuckle. A coil spring surrounds the shock absorber. The lower end of the coil spring is connected to the shock absorber via a coil spring seat. A support bearing, with a receiving body, receives the upper end winding of the coil spring. The support bearing is rigidly connected to the winding. A rolling-contact bearing is connected to the receiving body on one side and is connected to the car body on the other side. The rolling-contact bearing enables rotation of the coil spring during the steering movement of the wheels.
WO 89/05242 discloses a McPherson suspension strut which has a support bearing with a receiving body connected to the support bearing and a coil spring. Here, the receiving body receives the bearing race on the side of the spring of the support bearing. The receiving body is supported by a multitude of ribs distributed over the front side of the receiving body. The receiving body has formations corresponding to the spring against the end winding of the coil spring. The coil spring axis is arranged at an angle relative to the shock absorber axis.
DE 35 01 106 A1 discloses an arrangement with a support bearing and a coil spring for suspension struts. The winding diameter of the coil spring decreases in the upper area down to the mean diameter of the bearing mounted on the side of the car body. The coil spring elastically supports the piston rod of the shock absorber. Here, the axis of the coil spring is inclined to the outside relative to the axis of the shock absorber. This alignment enables a better transversal force compensation. The transversal forces are absorbed by the radial ball bearing.
In suspension struts, where the end winding of the coil spring is supported directly on a support bearing, the force application line of the coil spring is arranged at an angle relative to the axis of the shock absorber. In cases where the rolling-contact bearing, which is part of the support bearing, is arranged centered on the axis of the shock absorber, the interplay between the radial and the axial forces in the rolling-contact bearing is problematic. Due to the angled coil spring, radial forces also act on the rolling-contact bearing in addition to the axial forces. Here, the axial forces are not constant over the circumference of the winding end of the coil spring. Due to the manufacturing tolerances, the axial forces have their maximum at the winding end and between the winding end and the end of the abutment face of the rolling-contact bearing or a minimum to the receiving body of the support bearing, respectively.
If the transversal force acting on the bearing, due to the coil spring arranged at an angle relative to the shock absorber, is introduced such that no axial force is present in the area of the force application line of the transversal force, the balls of the bearing are not held in position in the groove bottom. The balls can run out of the groove bottom which results in a radial displacement of the two bearing races. Because of this, the sealing rings, into which the bearing races are inserted, can contact each other and an increased torque can be produced. Again, the increased force can lead to a degradation of the steering function and a reduction of the life time of the support.
It is an object of the present invention to provide a coil spring and support bearing arrangement for suspension struts supporting steering knuckles, where the transmission of the force acting from the coil spring onto the support bearing is optimized when the force application line of the coil spring is offset relative to the axis of the rolling-contact bearing of the support bearing.
A coil spring and a support bearing have a bearing centered on a first axis. A first receiving body is centered on the first axis and is arranged below the bearing and receives the bearing. A coil spring, having a force application line, is arranged at an angle relative to the first axis. An end winding of the coil spring at least partially winds around the first insertion body. The end winding end faces the rolling-contact bearing and has a winding end. The winding end lies within the area of a predetermined angle to a first plane. The angle is formed by the force application line and by the first axis. The first plane represents the bisector of the angle.
In this embodiment, the axial forces, which pretension the rolling-contact bearing to achieve a contact of the balls with the bearing races, have their maximum in the area of the force application line of the transversal force. This effectively prevents the balls of the rolling-contact bearing from run out off the grooves formed by the bearing races which, in turn, would lead to degradation of the bearing function and to reduction of the lifetime. Since the coil spring directly abuts the receiving body, the construction is simplified, which leads to a reduction of the manufacturing costs.
According to a further aspect of the present invention, the coil spring has a first portion which starts from the winding end. The first portion has at least a constant radius over a predetermined winding angle around the axis. The first portion of the coil spring is arranged in a second plane perpendicular to the axis. The radius of the first portion of the coil spring is approximated to the radius of the rolling-contact bearing. Because of this arrangement, the spring force can be directly introduced into the rolling-contact bearing without using additional components.
In accordance with the following aspect of the present invention, the coil spring has a cranked second portion continuous with the first portion of the end winding. The second portion increases the radius of the coil spring where the coil spring leaves the second plane. Because of the cranking of the coil spring, winding angles of the end winding around the first receiving body or the rolling-contact bearing of 200xc2x0 or more are achievable, respectively. Thus, the spring force can achieve a uniform force distribution along a large winding angle onto the rolling-contact bearing.
In a further embodiment, a damping body is arranged between the first portion of the coil spring and the bearing receiving body. The damping body prevents transmission of vibration onto the car body of the automobile, increasing driving comfort.
Preferably, the rolling-contact bearing is formed as an axial rolling-contact bearing or as an angular contact ball bearing. Generally, axial forces of the coil spring act on the rolling-contact bearing.
In a further preferred embodiment, the winding end is positioned in a predetermined angle bisected by the first plane, which is formed by the force application line of the coil spring and the axis, and the predetermined angle equals 30xc2x0. This has the advantage that the axial forces acting from the coil spring onto the rolling-contact bearing have their maximum in the area of the winding angle. Also, the transversal forces, resulting from the offsetting of the coil spring relative to the axis, are acting in this area. Thus, the winding end is arranged on the side of the angle of attack of the force application line relative to the first axis or on the side facing away from the angle of attack.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.